Measurement of moisture content of materials

ABSTRACT

An RF signal field is established through a partially conductive material, such as tobacco having a positive moisture content, and variations in the strength of the field, in response to change in the moisture content, are detected. The probe contacting the material is constructed with three conductive elements, the middle of which is grounded to provide measurements only of the strength of the RF field through the tobacco.

United States Patent 1191 [111 3,811,087 Schmelzer May 14, 1974MEASUREMENT OF MOISTURE CONTENT 3.400331 9/1968 Harris 324/6! P OFMATERIALS FOREIGN PATENTS OR APPLICATIONS [751 Inventor: schmelle"Town), 1,063,515 3/1967 Great Britain 384/6! P t Canada l,|49,650 4/l969Great Britain... Assigneez Rothmans of Paul Ma" Canada 19,050 9/1963Japan 324/61 P Limited, Ontario, Canada E S I T K Primary xaminertan eyrawczewicz [22] Fled: May 1973 Attorney, Agent, or Firm-Sim & McBurney[2]] Appl. No.: 361,899

[57] ABSTRACT S 324/58'5 z g z An RF signal field is established througha partially [58] i 58 61 P conductive material, such as tobacco having apositive 0 earc 4/ moisture content, and variations in the strength ofthe field, in response to change in the moisture content, are detected.The probe contacting the material is [56] References C'ted constructedwith three conductive elements, the mid- UNITED STATES-PATENTS dle ofwhich is grounded to provide measurements 2,435,880 2/1948 Eilenbergeruln 324/61 P only of the strength of the RF field through the to-2,950,436 8/l960 Butticaz et a]. bacco. 3,043,993 7/1962 Maltby3,079,55l 2/l963 Walker 324/58 A X 2 Claims, 4 Drawing FiguresPATENIEIIII/IY I4 I974 I SOURCE TOBACCO MONITORING TO CIGARETTE DEVICEMAKER 12 FIG. I

30 I6 32 34 I k I 2 RF SIGNAL OSCILLATOR PROBE AMPLIFIER METERoperation.

MEASUREMENT OF MOISTURE CONTENT OF MATERIALS FIELD OF INVENTION Thepresent invention is directed to the measurement of the moisture contentof materials, more particularly to the measurement and monitoring of themoisture content of tobacco.

BACKGROUND TO THE INVENTION SUMMARY OF INVENTION In the presentinvention an RF signal field is established through the tobacco andvariations in the strength of the field, in response to changes in themoisture content of the tobacco, are detected.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic representation ofone embodiment of the present invention;

FIG. 2 is a schematic representation of the monitoring device shown inFIG. 1;

FIG. 3 is a perspective view of the probe of FIG. 2; and

FIG. 4 is a sectional view of the probe of FIG. 3 in DESCRIPTION OFPREFERRED EMBODIMENTS In the drawings, tobacco whose moisture content isto be measured is passed from a source of tobacco 10 by line 12 througha moisture-content monitoring device 14, the tobacco thereafter beingpassed to a cigarette maker. This embodiment is described with themoisture content of the tobacco prior to passage thereof to thecigarette maker. The monitoring may occur at any other convenientlocation in the manufacture of the cigarettes, and more than one suchmonitor ing may occur.

The moisture content of the tobacco is monitored continuously by thedevice 14 and any detected deviation of the moisture content of thetobacco from predetermined limits may be corrected for the tobaccopassing to the cigarette maker and for the tobacco in the source.

The monitoring device 14 includes a probe 16 which contacts the tobaccostream 18 as it passes through the v monitoring device 14. The probe 16includes a base block 20 constructed substantially of electricallyinsulating material of low .dielectric constant and having a smooth flatface 22 contacting the tobacco stream 18.

Embedded in the base block 20 are two horizontally spaced-apartsubstantially parallel electrically conducting elements 24 and 26. Theelements 24 and 26 are positioned close to the face 22 and areelectrically insulated from each other.

The elements 24 and 26 may be in any convenient form, preferablyelongate strips in the manner illustrated. In addition, a thirdelectrically conductive element 28 is embedded in the base block 20,theelement 28 being positioned between and substantially parallel to theelements 24 and 26. The element 28 is positioned close to the face 22and preferably is in the form of an elongate strip, as illustrated, thestrips forming the elements 24, 26 and 28 being located in the sameplane, the plane being parallel to the face 22.

The element 24 is electrically connected to an oscillator 30 which maybe of any convenient construction to provide a highly stabilized RFsignal to the element 24.

As the tobacco passes in contact with the probe 16 an RF field isestablished through the tobacco stream 18 between the elements 24 and26. The strength of this field depends on the moisture content of thetobacco and will vary in accordance with variations in the moisturecontent. 7

The element 26 is electrically connected to an amplifier 32 to amplifythe RF signal received at the element 26 to a recordable level. Theamplifier may be of any convenient construction.

A recording device, typically a meter 34, is electrically connected tothe amplifier 32 whereby the strength of the RF signal field between theelements 24 and 26 may be detected. The meter 34 is suitably calibratedto indicate visually the detected variations and to indicate readingsoutside predetermined limits.

The RF signal passes between the elements 24 and 26 only through thetobacco. The strength of the field varies with the variations in themoisture content. The amplified variations are detected by the meter 34,which is suitably calibrated. Any detected variations beyond thepredetermined limits for the tobaccomay then be adjusted accordingly.

While this monitoring-system as just described operates satisfactorilyover short periods of time, it has been found that on prolonged use asubstantially continuous layer of moisture tends to form on the face 22of the probe 16. The presence of this layer causes the RF signal to passmainly directly from the element 24 to the element 26 through the layer,thereby rendering ineffective the monitoring of the moisture contentwith the tobacco.

In accordance with the present invention this is over-.

come in a particular manner. Thus, the third element 28 is earthed asshown schematically at 36 and this has the effect of interrupting thepassage of the field directly between the elements 24 and 26. Thus, evenin the presence of a layer of water on the face 22, the only variationsin the strength of the RF field measured are those through the tobaccostream 18.

The. presence of the earthed element 28 does reduce considerably theoverall strength of the RF signal field, indicated schematically by thearrows38 in FIG. 4, but this reduction in strength may be compensated bythe use of a suitably-powered amplifier 32. The presence of the earthedelement 28 therefore allows the monitoring device 14 to monitorcontinuously on a long term basis variation in the conductivity of thetobacco itself, and therefore the moisture content thereof, in thestream 18, irrespective of the accumulation of a very conducof thetobacco layer passing in contact with the probe.

The above-described system, while particularly useful in monitoring themoisture content of tobacco, may

be used to monitor. the moisture content of any other desired material,such as cereal, dog food, etc.

Modifications are possible within the scope of the present invention.

What I claim is: 1. A measuring device for measuring the moisturecontent of a material comprising probe means adapted to contact saidmaterial, said probe means including a block of electrically insulatingmaterialof low dielectric constant having a smooth, planarmaterial-engaging surface,

first, second and third elongated strips of conductive material embeddedin said block in parallel spacedapart manner, the plane of location ofsaid first, second and third elongate elements being substantiallyparallel to said planar material engaging surface,

said third elongate element being located between said first and secondelongate elements,

means establishing a highly stabilized RF signal at said first elongateconductive element and means connected to said second elongateconductive element for measuring the strength of the RF signal passingbetween said first and second elongate conductive elements throughmaterial in contact with said material-contacting surface in response tothe moisture content of said material, and means grounding said thirdelongate conductive element to earth'whereby said RF signal passingbetween said first and second elongate conductive elements follows anarcuate path through the material. 2. A method of monitoring themoisture content of tobacco which comprises continuously feeding astream of tobacco having a finite moisture content from a source thereofthrough a monitoring zone, providing in said monitoring zone a probeincluding a block of electrically insulating material of low dielectricconstant having a smooth planar surface in contact with which saidtobacco flows, said probe includingfirst, second and third elongatestrips of conductive material embedded in said block in parallelspaced-apart manner, the plane of location of said first, and thirdelongate elements being substantially parallel to said planar surface,said third elongate element being located between said first and secondelongate elements, continuously providing a highly stabilized RF signalto said first elongate element, 7 continuously maintaining an RF signalfield along a conductive path between said first and second elongateelements, continuously maintaining said third elongate element groundedto earth to short any conductive path directly between said first andsecond elongate elements, whereby said field is maintained through saidtobacco,'and continuously detecting changes in the strength of said RFsignal field through said tobacco in response to changes in the moisturecontent of said tobacco.

1. A measuring device for measuring the moisture content of a materialcomprising prObe means adapted to contact said material, said probemeans including a block of electrically insulating material of lowdielectric constant having a smooth, planar material-engaging surface,first, second and third elongated strips of conductive material embeddedin said block in parallel spaced-apart manner, the plane of location ofsaid first, second and third elongate elements being substantiallyparallel to said planar material engaging surface, said third elongateelement being located between said first and second elongate elements,means establishing a highly stabilized RF signal at said first elongateconductive element and means connected to said second elongateconductive element for measuring the strength of the RF signal passingbetween said first and second elongate conductive elements throughmaterial in contact with said material-contacting surface in response tothe moisture content of said material, and means grounding said thirdelongate conductive element to earth whereby said RF signal passingbetween said first and second elongate conductive elements follows anarcuate path through the material.
 2. A method of monitoring themoisture content of tobacco which comprises continuously feeding astream of tobacco having a finite moisture content from a source thereofthrough a monitoring zone, providing in said monitoring zone a probeincluding a block of electrically insulating material of low dielectricconstant having a smooth planar surface in contact with which saidtobacco flows, said probe including first, second and third elongatestrips of conductive material embedded in said block in parallelspaced-apart manner, the plane of location of said first, and thirdelongate elements being substantially parallel to said planar surface,said third elongate element being located between said first and secondelongate elements, continuously providing a highly stabilized RF signalto said first elongate element, continuously maintaining an RF signalfield along a conductive path between said first and second elongateelements, continuously maintaining said third elongate element groundedto earth to short any conductive path directly between said first andsecond elongate elements, whereby said field is maintained through saidtobacco, and continuously detecting changes in the strength of said RFsignal field through said tobacco in response to changes in the moisturecontent of said tobacco.